1. Field of the Invention
The invention relates to a colour display device for monovalve projectors, especially a trichromatic device, and to its method of production.
2. Discussion of the Background
In order to obtain large-sized video pictures, one alternative solution to the cathode-ray tube, which then becomes heavy and bulky, is projection using liquid-crystal valves (liquid-Crystal Display or LCD). An LCD projector operates according to the principle of a slide projector, the LCD valve or valves replacing the slides.
The colour picture may be obtained either from three monochromatic screens each illuminated by one of the three primaries, red, green or blue, or by a single valve whose pixels (picture elements) are equipped with colour filters which transmit only one of the primaries. One colour point then consists of three monochromatic subpixels.
The architecture of a monovalve projector, which uses a single valve with colour filters, is very simple. It comprises a lamp, an LCD valve and a projection objective. However, it also has a certain number of drawbacks including:
a low light yield: approximately 2/3 of the light is stopped by the colour filters which let through only a single colour for which they have, in addition, a non-negligible absorption; PA1 the LCD valve is difficult to produce, on account of the delicate technology of colour filters inserted into the liquid-crystal cells. PA1 at least one light source emitting several primary wavelengths; PA1 an array of holographic lenses; PA1 a spatial light modulator comprising one pixel (picture element) per lens, each pixel comprising one subpixel per primary wave to be displayed; PA1 each lens in the array dispersing and focusing the various primaries, each in a subpixel. PA1 a layer of a holographic material is produced; PA1 a reference light wave and at least one cylindrical or spherical light wave are made to interfere in the layer of holographic material, both these waves having the same recording wavelength, thus producing at least one holographic lens which can be read again by a second light wave under conditions close to the Bragg conditions; PA1 a spatial light modulator is associated in the focal plane of the holographic lens for a chosen wavelength.
The invention relates to a liquid-crystal-monovalve colour display device enabling these drawbacks to be alleviated.